Systematic occurrence cycle of typical RH-profiles during the MJO: evidence for ubiquitous pre-moistening

We describe how typical relative humidity (RH) profiles change systematically through the phases of the Madden–Julian Oscillation (MJO). We use 18 years of classified RH-profiles from the Atmospheric Infrared Sounder, clustered without prior knowledge of large-scale dynamics or occurrence-region. Occurrence probability (OP) anomalies of RH-profiles classes exhibit classical MJO patterns: Large positive OP anomalies of the RH-profile class with most moisture in the free troposphere are co-located with the largest positive precipitation anomalies. About 10 days prior to this deep convective core large OP anomalies of a RH-profile class occur consistent with lower atmospheric moistening, supporting a ubiquitous role of pre-moistening in MJO propagation. Since each RH-profile class is associated with distinct dynamics (most of which are subgrid-scale to climate models) our results can serve as process-based diagnostics to investigate parameterization shortcomings of climate models preventing them to simulate the MJO accurately.